https://www.soundandvision.com/content/tube-amps-pocket-change-nobsound-ns-08e
fitted with Nos RTC 5654 RT tube sound fantastic with HD 800s.
It cost me around 100 bucks including Nos tube and adapter.
https://www.amazon.com/gp/product/B078X85LFS/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
This combination of Nob and 800s sounds more natural and pleasing than Raal Sr1a driven by Jot R while the latter sounds more open and exciting but close to hot.
This one also may work well HD600.